Switching device for a pixel electrode and methods for fabricating the same

ABSTRACT

The invention discloses a switching element of a pixel electrode for a display device and methods for fabricating the same. A gate is formed on a substrate. A first copper silicide layer is formed on the gate. An insulating layer is formed on the first copper silicide layer. A semiconductor layer is formed on the insulating layer. A source and a drain are formed on the semiconductor layer. Moreover, a second copper silicide layer is sandwiched between the semiconductor layer and the source/drain.

BACKGROUND

The invention relates to a display device, and more particularly to a switching device for a pixel electrode and methods for fabricating the same.

Bottom-gate type thin film transistors (TFTs) are widely used for thin film transistor liquid crystal displays (TFT-LCDs). FIG. 1 is a sectional view of a conventional bottom-gate type TFT structure 100. The TFT structure 100 typically comprises a glass substrate 110, a gate 120, a gate-insulating layer 130, a channel layer 140, an ohmic contact layer 150, a source 160 and a drain 170.

As the size of TFT-LCD panels increases, metals having low resistance are required. For example, gate lines employ low resistance metals such as Cu and Cu alloy in order to improve operation of the TFT-LCD.

However, Cu can react with radicals to form Cu oxide in subsequent processes, thereby increasing resistance. Also, Cu diffuses easily and reacts with silicon to form CuSi_(x), significantly affecting reliability of the device.

JP 2000-332015, the entirety of which is hereby incorporated by reference, discloses a method of forming CuSi_(x). A layer of CuSi_(x) is formed between a silicon-rich nitride layer and a Cu layer, enhancing adhesion therebetween.

SUMMARY

Thin film transistors and fabrication methods thereof are provided. Diffusion of Cu is reduced, and no extra processes such as photolithography are required.

An embodiment of a fabrication method comprises forming a gate on a substrate. A first CuSi_(x) layer is formed on the gate by plasma treatment on the gate in a silane-containing chamber. The temperature of the chamber is substantially about 180° C. to 370° C.

To enhance the barrier properties of the first CuSi_(x) layer, a subsequent plasma treatment is performed on the first CuSi_(x) layer in a chamber containing N₂ and NH₃. The temperature of the chamber is substantially about 180° C. to 370° C.

An insulating layer is formed on the first CuSi_(x) layer. A semiconductor layer is formed on the insulating layer. A source and a drain are formed on the semiconductor layer. A pixel electrode is formed, electrically connecting to the source or the drain.

Another embodiment of a method comprises forming a second CuSi_(x) layer between the semiconductor layer and the source/drain.

Formation of the second CuSi_(x) layer comprises forming a Cu layer or a Cu alloy layer on the semiconductor layer and performing a plasma treatment on the Cu layer or the Cu alloy layer in a silane-containing chamber. The temperature of the chamber is substantially about 180° C. to 370° C.

To enhance the barrier properties of the second CuSi_(x) layer, a subsequent plasma treatment is performed on the second CuSi_(x) layer in a chamber containing N₂ and NH₃. The temperature of the chamber is substantially about 180° C. to 370° C.

In these embodiments, the first CuSi_(x) layer is conformally formed on the gate. The substrate comprises a glass substrate. The insulating layer comprises a silicon oxide, silicon nitride, silicon oxynitride, tantalum oxide or aluminum oxide layer. The semiconductor layer comprises silicon. The source/drain comprises Cu or Cu alloy.

Thin film transistors (TFTs) of the invention can be bottom-gate or top-gate, serving as a switching device for a pixel electrode when the source/drain are electrically in contact with a pixel electrode. In addition, the TFTs of the invention can be applied in display such as LCD.

DESCRIPTION OF THE DRAWINGS

The invention can be more fully understood by reading the subsequent detailed description in conjunction with the examples and references made to the accompanying drawings.

FIG. 1 is a sectional view of a conventional TFT structure.

FIGS. 2A to 2F are sectional views of an exemplary process for fabricating a first embodiment of a TFT structure of the present invention.

FIGS. 3A to 3H are sectional views of an exemplary process for fabricating a second embodiment of a TFT structure of the present invention.

DETAILED DESCRIPTION First Embodiment

An exemplary process for fabricating a first embodiment of TFTs of the invention is shown in FIGS. 2A-2F.

In FIG. 2A, a Cu layer (not shown) is formed on a substrate 210, for example, by chemical vapor deposition (CVD), electrochemical plating (ECP), or physical vapor deposition (PVD). The Cu layer is deposited, forming a gate 220 on the substrate 210. The substrate 210 may be a glass substrate. The gate 220 may be copper with thickness substantially about 100 nm to 500 nm.

In FIGS. 2B and 2C, a first CuSi_(x) layer 227 is conformally formed on the gate 220 by plasma treatment 225 of the gate 220 in a silane-containing chamber. The temperature of the chamber is substantially about 180° C. to 370° C. Silicon atoms react with the surface of the gate 220 of Cu, forming the first CuSi_(x) layer 227, preventing Cu from diffusing to the insulating layer 230 shown in FIG. 2E. The thickness of the first CuSi_(x) layer 227 is substantially about 5 nm to 100 nm.

In FIG. 2D, a subsequent plasma treatment 225 a is performed on the first CuSi_(x) layer 227 in a chamber containing N₂ and NH₃. The temperature of the chamber is substantially about 180° C. to 370° C. Nitrogen atom reacts with the surface of the first CuSi_(x) layer 227 to form N—Si bond, thereby enhancing the barrier properties of the first CuSi_(x) layer.

In FIG. 2E, an insulating layer 230 is formed on the first CuSi_(x) layer 227. A semiconductor layer (not shown) is formed on the insulating layer 230. The insulating layer 230 comprises silicon oxide, silicon nitride, silicon oxynitride, tantalum oxide or aluminum oxide. The semiconductor layer comprising a channel layer 240 and an ohmic contact layer 250 is defined on a portion of the gate-insulating layer 230 by deposition and patterning. The channel layer 240 can be an undoped amorphous silicon layer formed by CVD. The ohmic contact layer 250 can be an impurity-added silicon layer formed by CVD. The impurity can be n type dopant (for example, P or As) or p type dopant (for example, B).

In FIG. 2F, a Cu layer (not shown) is formed on the ohmic contact layer 250, for example, by CVD, ECP, or PVD. The source/drain 260/270, of Cu or Cu alloy, are formed on the ohmic contact layer 250 by selectively etching through the Cu layer, the ohmic contact layer 250, exposing a portion of the surface of the channel layer 240. A pixel electrode is formed, electrically connected to the source/drain 260/270. A resultant thin film transistor 200 is obtained.

Second Embodiment

An exemplary process for fabricating a second embodiment of TFTs of the present invention is shown in FIGS. 3A-3H.

In FIG. 3A, a Cu layer (not shown) is formed on a substrate 210, for example, by chemical vapor deposition (CVD), electrochemical plating (ECP), or physical vapor deposition (PVD). The Cu layer is etched, forming a gate 220 on the substrate 210. The substrate 210 may be a glass substrate. The gate 220 may be copper with thickness substantially about 100 nm to 500 nm.

In FIGS. 3B and 3C, a first CuSi_(x) layer 227 is conformally formed on the gate 220 by performing plasma treatment 225 of the gate 220 in a silane-containing chamber. The temperature of the chamber is substantially about 180° C. to 370° C. Silicon atoms react with the surface of the gate 220 of Cu, forming the first CuSi_(x) layer 227, preventing Cu from diffusing to the insulating layer 230 shown in FIG. 3E. The thickness of the first CuSi_(x) layer 227 is substantially about 5 nm to 100 nm.

In FIG. 3D, a subsequent plasma treatment 225 a is performed on the first CuSi_(x) layer 227 in a chamber containing N₂ and NH₃. The temperature of the chamber is substantially about 180° C. to 370° C. Nitrogen atom reacts with the surface of the first CuSi_(x) layer 227 to form N—Si bond, thereby enhancing the barrier properties of the first CuSi_(x) layer.

In FIG. 3E, an insulating layer 230 is formed on the first CuSi_(x) layer 227. A semiconductor layer (not shown) is formed on the insulating layer 230. The insulating layer 230 comprises silicon oxide, silicon nitride, silicon oxynitride, tantalum oxide or aluminum oxide. The semiconductor layer comprising a channel layer 240 and an ohmic contact layer 250 is defined on a portion of the gate-insulating layer 230 by deposition and patterning. The channel layer 240 can be an undoped amorphous silicon layer formed by CVD. The ohmic contact layer 250 can be an impurity-added silicon layer formed by CVD. The impurity can be n type dopant (for example P or As) or p type dopant (for example B).

In FIG. 3E, a Cu layer 252 is formed on the ohmic contact layer 250, for example, by CVD, ECP, or PVD.

In FIGS. 3F and 3G, a Cu layer 252 is formed on the semiconductor layer. In other embodiments, a Cu alloy layer can be formed in place of the Cu layer. Plasma treatment is performed on the Cu layer 252, completely forming a second CuSi_(x) layer 252 a. The second CuSi_(x) layer 252 a prevents diffusion of Cu from the source/drain 260/270 shown in FIG. 3H to the underlying substrate. The plasma treatment 254 is performed in a silane-containing chamber. The temperature of the chamber is substantially in a rang of about 180° C. to about 370° C. The thickness of the second CUSi_(x) layer 252 a is substantially in a rang of about 5 nm to 100 nm.

In FIG. 3G, a subsequent plasma treatment 254 a is performed on the second CuSi_(x) layer 252 a in a chamber containing N₂ and NH₃. The temperature of the chamber is substantially about 180° C. to 370° C. Nitrogen atoms react with the surface of the second CuSi_(x) layer 252 a to form N—Si bond, thereby enhancing the barrier properties of the second CuSi_(x) layer.

In FIG. 3H, a Cu layer (not shown) is formed on the second CuSi_(x) layer 252 a, for example, by CVD, ECP, or PVD. The source/drain 260/270, of Cu or Cu alloy, is formed on the second CuSi_(x) layer 252 a by selectively etching through the Cu layer, second CuSi_(x) layer 252 a, the ohmic contact layer 250, exposing a portion of the surface of the channel layer 240. A pixel electrode is formed, electrically connecting to the source/drain 260/270. A resultant thin film transistor 300 is obtained.

While the invention has been described by way of example and in terms of preferred embodiment, it is to be understood that the invention is not limited thereto. On the contrary, it is intended to cover various modifications and similar arrangements as would be apparent to those skilled in the art. Therefore, the scope of the appended claims should be accorded the broadest interpretation so as to encompass all such modifications and similar arrangements. 

1. A switching element of a pixel electrode for a display device, comprising: a gate, comprising Cu or Cu alloy, formed on a substrate; an insulating layer formed on the gate; a first CuSi_(x) layer interposed between the gate electrode and the insulating layer, wherein the first CuSi_(x) layer is formed by performing a plasma treatment on the gate electrode in a silane-containing chamber; a semiconductor layer formed on the insulating layer; and a source and a drain formed on a portion of the semiconductor layer; wherein the switching element of a pixel electrode further comprises a second CuSi_(x) layer interposed between the semiconductor layer and the source/drain.
 2. The switching element of a pixel electrode according to claim 1, further comprising a pixel electrode electrically connected to the source or the drain.
 3. The switching element of a pixel electrode according to claim 1, wherein the first CuSi_(x) layer is conformally formed on the gate.
 4. The switching element of a pixel electrode according to claim 1, wherein thickness of the first CuSi_(x) layer is substantially about 5 nm to 100 nm.
 5. The switching element of a pixel electrode according to claim 1, wherein the source and the drain comprise Cu or Cu alloy. 